OPNsense
  • Home
  • Help
  • Search
  • Login
  • Register

  • OPNsense Forum »
  • English Forums »
  • General Discussion »
  • how to set up MTU properly; fragmented UDP packets getting truncated
« previous next »
  • Print
Pages: [1]

Author Topic: how to set up MTU properly; fragmented UDP packets getting truncated  (Read 3898 times)

CodingFiend

  • Newbie
  • *
  • Posts: 2
  • Karma: 0
    • View Profile
how to set up MTU properly; fragmented UDP packets getting truncated
« on: March 01, 2018, 09:04:03 pm »
I am getting a 1507 byte UDP packet, and as i set up OPNSense as a transparent bridge, my igb0 and ibg1 ethernet ports were set at the typical 1500 byte limit. But when a 1507 UDP packet comes in as a fragmented packet, the firewall ends up truncating the packet. Do i need to set the bridge port  (i think called OPT1) to have an MTU of 1492? I can't find any examples of how to do this correctly, and clearly i am getting screwed because i don't have the parameters set just right. Or do you set the MTU to 9000 across the board? TCP doesn't have this problem because TCP has a mechanism for determining MTU on a path, but UDP is a one shot, one way ticket on the information superhighway, so you gotta be careful...  or is this just a known bug in OPNSense whereby fragmented UDP packets are not handled correctly, and are silently truncated?

surely i can't be the first person to bump against this. A prize to whomever helps me resolve this.
« Last Edit: March 01, 2018, 09:22:51 pm by CodingFiend »
Logged

namezero111111

  • Jr. Member
  • **
  • Posts: 94
  • Karma: 10
    • View Profile
Re: how to set up MTU properly; fragmented UDP packets getting truncated
« Reply #1 on: December 16, 2020, 01:51:33 pm »
Digging this up.

Having run into this exact same problem (UDP SIP; options too large) passing through a transparent filtering bridge, have you ever found a solution to this issue?
Logged

  • Print
Pages: [1]
« previous next »
  • OPNsense Forum »
  • English Forums »
  • General Discussion »
  • how to set up MTU properly; fragmented UDP packets getting truncated
 

OPNsense is an OSS project © Deciso B.V. 2015 - 2024 All rights reserved
  • SMF 2.0.19 | SMF © 2021, Simple Machines
    Privacy Policy
    | XHTML | RSS | WAP2